1. Field of the Invention
The present invention relates generally to a method of grinding (lapping) a chiplet for forming a magnetic head(s) and the construction of thin-film magnetic heads. More particularly, this invention relates to: (a) a grinding (lapping) method where optical grinding markers are utilized for easy and accurate determination of the amount of working performed grinding a specified portion of a magnetic head to form the air bearing surface of the head; (b) thin film magnetic heads bearing such optical markers; and (c) a process for producing magnetic heads having such optical markers.
2. Description of the Background Information
In data processing systems, magnetic recording has been employed for storing large amounts of data on magnetic recording disks and magnetic tapes. In the case of the magnetic recording disks, data is read from and written onto the tracks by positioning magnetic transducers, commonly referred to as magnetic heads, adjacent to the tracks. In recent years, the requirement for higher data density on the magnetic recording medium has imposed a requirement to store more data on ever narrowing tracks. In order to read from and write onto such narrow tracks, a new type of head known as a thin-film magnetic head has been utilized where the magnetic head elements are formed from thin films of magnetic materials. These heads, which generally comprise a conductive core and are formed in layers on a substrate with an insulating layer interposed between adjacent conducting layers, are fabricated by thin film fabrication techniques such as vacuum evaporation, sputtering and photolithography. Thin film magnetic heads have the advantage that they can be made much smaller than conventional bulk-type material heads. Such thin film heads may also comprise magneto-resistive (MR) elements for reading data from tracks that are very narrow.
Since thin-film magnetic heads are much smaller than the bulk-type magnetic heads in the depth of the magnetic gap, in order to achieve maximum efficiency, that is, to achieve maximum amount of electrical signals from a given magnetic head element, the element must have a pole tip height dimension, commonly referred to as throat height for thin-film inductive heads, or element height in the case of a magneto-resistive read element, which must be maintained within a predetermined tolerance. A method of producing a required throat/element height for magnetic elements includes a coarse or fast grind step followed by a lapping or fine grind step.
U.S. Pat. No. 5,305,559, issued on Apr. 26, 1994, proposes a magnetic head structure, seen in FIG. 8 of this application, where a pair of first and second markers 32, 34 are formed by photolithography in the magnetic core. Each marker has two edges which are spaced from each other in a direction of width of the magnetic gap and further the two edges are located on the same side as viewed in the gap width direction. Markers 32a and 32b are formed in a V-shape and markers 34a and 34b are formed using two right-angle isosceles triangles.
In this method, grinding can only be monitored by measuring the first distance between the two edges of each marker which is exposed on the working surface under grinding, so as to determine a required residual depth of the grinding which is to be further effected to establish a nominal depth dimension of the magnetic gap. However, substantial time had to be taken using optical equipment with high precision in order to precisely measure the distance between the two edges of each marker which is exposed to the working surface under grinding.
U.S. Pat. No. 5,056,353, issued on Oct. 15, 1991, proposes a thin film magnetic head structure, as seen in FIG. 9 of this application, having a working amount detecting markers 6 formed by two thin films superposed in layers on the upper surface of a substrate in the form of a polygon. The contours of the respective thin film layers intersect each other at a point located at a specified position where working is to be completed. In this structure, the presence or absence of overlapping between the two marker layers appearing on the ground surface provides a rough visual indicator as to how far the workpiece has been lapped. Also, once the point of intersection appears on the ground surface, it indicates completion of grinding.
However, this structure requires two marker layers where the first marker layer is formed on the upper surface of the lower magnetic core and the second marker layer is formed over the first marker layer with an insulating layer interposed therebetween. Furthermore, while the working piece is being lapped, and while an operator is observing the configuration of the end face of the detecting markers, as they appear on the lapping surface, there is no indication as to how far the lapping process is from reaching the intersection point. Only by measuring the width of at least one marker layer having the side inclined with respect to the direction of progress of lapping, the amount of gap depth remaining to be lapped can be calculated.
Therefore, an invention is needed that provides accurate and easily available information in regard to how far the thin film head has been lapped or how much lapping remains to be performed using a low power microscope (20 to 100.times.magnification) without a need for making dimensional measurement(s) or the use of precision optical equipment such as a high power microscope.